The guys at Forgotten Weapons have done a great video which explains Machine Gun Terminology. Not only are there way too many different categories of machine guns, some of these terms have changed over time. Forgotten Weapons tells us who makes them, why they exist and their place in military history.

Photo courtesy of US Army. A New Jersey Army National Guard Soldier from fires his M249 SAW during live-fire battle drills on Joint Base McGuire-Dix-Lakehurst, N.J., April 9, 2018. (U.S. Air National Guard photo by Master Sgt. Matt Hecht)